Transient dynamic analysis of cracked structures with multiple contact pairs using generalized HSNC

Nonlinear Dynamics - The development of efficient computational methods for cracked structures is critical in the fields of civil, mechanical, and aerospace engineering since the influence of...     

Elimination mechanisms of Br(2)+ and Br+ in photodissociation of 1,1- and 1,2-dibromoethylenes using velocity imaging technique

Elimination pathways of the Br(2)(+) and Br(+) ionic fragments in photodissociation of 1,2- and 1,1-dibromoethylenes (C(2)H(2)Br(2)) at 233 nm are investigated using time-of-flight mass spectrometer equipped with velocity ion imaging. The Br(2)(+) fragments are verified not to stem from ionization of neutral Br(2), that is a dissociation channel of dibromoethylenes reported previously. Instead, they are produced from dissociative ionization of dibromoethylene isomers. That is, C(2)H(2)Br(2) is first ionized by absorbing two photons, followed by the dissociation scheme, C(2)H(2)Br(2)(+) + hv→Br(2)(+) + C(2)H(2). 1,2-C(2)H(2)Br(2) gives rise to a bright Br(2)(+) image with anisotropy parameter of -0.5 ± 0.1; the fragment may recoil at an angle of ～66° with respect to the C=C bond axis. However, this channel is relatively slow in 1,1-C(2)H(2)Br(2) such that a weak Br(2)(+) image is acquired with anisotropy parameter equal to zero, indicative of an isotropic recoil fragment distribution. It is more complicated to understand the formation mechanisms of Br(+). Three routes are proposed for dissociation of 1,2-C(2)H(2)Br(2), including (a) ionization of Br that is eliminated from C(2)H(2)Br(2) by absorbing one photon, (b) dissociation from C(2)H(2)Br(2)(+) by absorbing two more photons, and (c) dissociation of Br(2)(+). Each pathway requires four photons to release one Br(+), in contrast to the Br(2)(+) formation that involves a three-photon process. As for 1,1-C(2)H(2)Br(2), the first two pathways are the same, but the third one is too weak to be detected.     

Synthesis and biological evaluation of peptidyl organotrifluoroborates and their corresponding boron analogs

Six peptidyl organotrifluoroborates and their corresponding boronate esters and/or boronic acid analogs were designed and synthesized. Their anti-proliferative activity against hepatocellular carcinoma cells (HepG2) and human metastatic breast cancer cells (MDA-MB231) were evaluated by use of an MTT assay. Potassium {4-[(3S,6S,9S)-3,6-dibenzyl-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}trifluoroborate (B6) was potent (IC₅₀ = 29.9 μM) against MDA-MB231, and {4-[(3S,6S,9S)-6-benzyl-3-((benzyloxy)methyl)-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}boronic acid (B9) and Potassium {4-[(3S,6S,9S)-6-benzyl-3-((benzyloxy)methyl)-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}trifluoroborate (B10) had broad anti-proliferative activity against HepG2 (IC₅₀ = 24.7 and 21.8 μM, respectively) and MDA-MB231 (IC₅₀ = 24.5 and 18.9 μM, respectively).     

Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v = 1, 2) and CO(v = 1-3) are detected in one-photon dissociation of acetyl cyanide (CH(3)COCN) at 308 nm. The S(1)(A(")), (1)(n(O), π(?) (CO)) state at 308 nm has a radiative lifetime of 0.46 ± 0.01 μs, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) × 10(-12) cm(3) molecule(-1) s(-1). The measurements of O(2) dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 ± 7 and 32 ± 3 kJ∕mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH(2)CO, in which the CH(2)CO moiety may further undergo secondary dissociation to release CO. The production of CO(2) in the reaction with O(2) confirms existence of CH(2) and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH(3) fragments that dominate the dissociation products at 193 nm are not detected.     

Three-dimensional printed knotted reactors enabling highly sensitive differentiation of silver nanoparticles and ions in aqueous environmental samples

Whether silver nanoparticles (AgNPs) persist or release silver ions (Ag⁺) when discharged into a natural environment has remained an unresolved issue. In this study, we employed a low-cost stereolithographic three-dimensional printing (3DP) technology to fabricate the angle-defined knotted reactors (KRs) to construct a simple differentiation scheme for quantitative assessment of Ag⁺ ions and AgNPs in municipal wastewater samples. We chose xanthan/phosphate-buffered saline as a dispersion medium for in situ stabilization of the two silver species, while also facilitating their extraction from complicated wastewater matrices. After method optimization, we measured extraction efficiencies of 54.5 and 32.3% for retaining Ag⁺ ions and AgNPs, respectively, in the printed KR (768-turn), with detection limits (DLs) of 0.86 and 0.52 ng L⁻¹ when determining Ag⁺ ions and AgNPs, respectively (sample run at pH 11 without a rinse solution), and 0.86 ng L⁻¹ when determining Ag⁺ ions alone (sample run at pH 12 with a 1.5-mL rinse solution). The proposed scheme is tolerant of the wastewater matrix and provides more reliable differentiation between Ag⁺/AgNPs than does a conventional filtration method. The concept and applicability of adopting 3DP technology to renew traditional KR devices were evidently proven by means of these significantly improved analytical performance. Our analytical data suggested that the concentrations of Ag⁺ ions and AgNPs in the tested industrial wastewater sample were both higher than those in domestic wastewater, implying that industrial activity might be a main source of environmental silver species, rather than domestic discharge from AgNP-containing products.     

Direct synthesis of the arylboronic acid analogues of phenylglycine via microwave-assisted four-component Ugi reaction

A four-component Ugi reaction (Ugi-4CR) utilizing formylphenyl boronic acids under mild condition was developed for the synthesis of arylboronic acid analogs. The reactions were performed in methanol and accelerated by microwave irradiation, which makes this strategy suitable for constructing boronic-containing chemical libraries. Two of the synthesized analogs were found to have cytotoxic activity against HepG2, MDA-MB231, and A549 cancer cell lines, demonstrating the potential application of this approach in developing novel boron-containing pharmaceuticals.     

Fabrication and superhydrophobicity of fluorinated titanium dioxide nanocoatings

This study demonstrates the fabrication of a stable superhydrophobic surface with low contact angle hysteresis (CAH) using an arrangement of nanoscale TiO₂ spheres. The control of precursor quantity is selected as the key factor in determining surface roughness that significantly intensifies water contact angle (CA) of TiO₂ films. After surface fluorination treatment, the anatase-type crystalline surfaces exhibit good water repellency (CA 166.1°), low CAH (6°), and superhydrophobic stability (>60 min). Enhanced water repellency is attributed to the fact that the higher density of TiO₂ spheres results in more tortuous three-phase contact line, leading to the self-cleaning effect. Such a unique textured surface imparts many promising potentials for engineering and the development of optics devices with robust superhydrophobic materials.     

Synthesis of Ugi-4CR boronate analogues via microwave irradiation

The synthetic condition for the synthesis of boronate ester Ugi-4CR analogs under mild conditions was developed. The reported reactions were carried out in methanol and promoted by microwave heating. This synthetic strategy could provide unique access to a broad range of boron-containing chemical libraries.     

Molecular elimination of methyl formate in photolysis at 234 nm: roaming vs. transition state-type mechanism

Ion imaging coupled with (2 + 1) resonance-enhanced multiphoton ionization (REMPI) technique is employed to probe CO(v″ = 0) fragments at different rotational levels following photodissociation of methyl formate (HCOOCH(3)) at 234 nm. When the rotational level, J″(CO), is larger than 24, only a broad translational energy distribution extending beyond 70 kcal mol(-1) with an average energy of about 23 kcal mol(-1) appears. The dissociation process is initiated on the energetic ground state HCOOCH(3) that surpasses a tight transition state along the reaction coordinate prior to breaking into CO + CH(3)OH. This molecular dissociation pathway accounts for the CO fragment with larger rotational energy and large translational energy. As J″(CO) decreases, a bimodal distribution arises with one broad component and the other sharp component carrying the average energy of only 1-2 kcal mol(-1). The branching ratio of the sharp component increases with a decrease of J″(CO); (7.3 ± 0.6)% is reached as the image is probed at J″(CO) = 10. The production of a sharp component is ascribed to a roaming mechanism that has the following features: a small total translational energy, a low rotational energy partitioning in CO, but a large internal energy in the CH(3)OH co-product. The internal energy deposition in the fragments shows distinct difference from those via the conventional transition state.